Tuning device for true antennas



July 18, 1950 F. B ABlN 2,515,436

TUNING DEVICE FOR TRUE ANTENNAS Filed Oct. 3, 1946 2 Sheets-Sheet 1(REACTANCE) mss siAucz) 0 Y 1 (REACTANCE) (RESISTANCE) 0 X INVENTORFRANCOIS BABIN July 18, 1950 F. BABIN 2,515,436

TUNING DEVICE FOR TRUE ANTENNAS Filed Oct. s, 1946 v 2 Sheets-Sheet 2 INVENTOR FRANCOIS BABl N BY &

NEY

Patented July 18, 1950 TUNING DEVICE FOR TRUE ANTENNAS Y FrancoisBabin,Paris, France, assignor to La 'Radio-Industn'e, Paris, France, a.society of France.

Application October 3, 1946, Serial No. 701,043 In France October 4,1945 .3 Claims. (c1. 250-33 The presentr'invention relates to tuning"devices for true antennas, the expression true-antennas being used :to:differentiate them from artificial orfdummy antennas, the inventionbeing more especially concerned with the case when said antennas" areused to work on Wave-lengths shorterthan four timestheir length.

Itis known that an-antenna-when it is used towork.ondifierentiwavedengths, and in particular wave-lengthsrshorterthan four times its length, has atotaliimpedancewhich consists of twoportions, to wit: an active one (resistance to radiation)and alreactiveone (reactance). The adjustment or tuning of this antenna is theoperation. whichconsists in adding thereto circuits such that,with'little losses, the impedance'thereof is caused to assume a purelyactive form and a predetermined value. i

This result is generally-obtained by proceeding in two steps; thefirst-ste consists in reducing the reactance to-zero by inserting inseries with the antenna inductance coils or capacitors, according to thedirection of this reac'tance; the second step transforms the newimpedance thus obtained, for instance by circuit coupling.

The -chief object of invention is to provide a tunin device of 'the kindabove referred to which isbetter adapted to meet the variousrequirementsof practice'than those used up to this time, in particularwhich permits of tuning the antenna in a single'operation.

Preferred embodimentsof invention will be hereinafter described withreference to the accompanying drawings, given mer'ely'by way of exampleand inwh-ich: Y a

Fig, 1 showsa curve representing the-variation of the total impedance ofan antennawhenthe wa-ve-length-varies; I i

Fig: 2- shows a portion of the same curve on-a difierent' scale;

Fig. 3, diagrammatically shows ,a: system of tuning circuits accordingto theinvention';

Fig. 4;; diagrammatically shows another system oftuning circuits'also.accordingto the invention.

It'is known thatjwhen an antenna is caused to work on wave-lengthsshorter than i'our times its length, the variations of its impedancewhen the wave-length varies may be represented by a curve such asvthat'of Fig. l, by plotting in abscissas the active resistance; and in.ordinates the reactance. The theoretical curve in question is a spiralwhich intersects thea-xis ofabscissas, at points grouped in two series,to wit: so-called'resonanc points, of low impedance, and so-calledanti-resonance points, of high impedance.

' For practical purposes, this curve may be considered as constitutedbya Set of semi-circles, alternately located on one side and the otherofthe axis of abscissas OX having their centers on this axis, andextending each from a resonance point to the next anti resona-nce point.On such a curve I (Fig. 1), the pointthat represents the antennaimpedance travels in the direction of arrow F when the wave-lengthdecreases, point A being the representative point for the antennaworking in quarter-wave fashion. Theory and experience show that thegeometrical power of origin point 0 with reference to all these circlesis approximately equal to the characteristic impedance Z of the antennathat is utilized. a a 1 Being givenwan' antenna'of characteristicimpedance Z, the point that represents its total impedance for thewave-length on which it is caused to work is for instance locatedatM,--'on a circle of center 33 (Fig. 2).

Up to now, tuning the antenna consisted in bringing the figurative pointfrom M to N, then from N to a point P, upon the axis-"OX of the activeresistances.

The essential feature of the present invention consists in providing, inseries with the antenna, circuits including inductance coils andcapacitors and adjusting the values of said inductance coils andcapacities simultaneously and in such manner that the point thatrepresents this total impedance travels along the impedance curve towardthe first resonance point that is reached when turning in the clockwisedirection.

This result can be obtained by making use of an adjustable feeder havinglike the antenna (to ensure the minimum of losses) a characteristicimpedanceequal td-Z.

By varying the working length of this feeder without modifying itscharacteristic impedance, its inductance and its capacityare'causedsimultaneously to vary. Consequently the. point M that represents theantenna impedance for the wave-length that its utilizedwill becaused totravel'on the circle above defined so as to come to the nearestresonancepoint Q.

Preferably, the feederincludes a pluralityof suitably grouped variableelements for adjustment thereof. I

' For instance,'as shown'by Fig. 3,'it. consists of a line includinginductance coils Lin series with antenna Land capacitors C in shunt withthe earth 3. All these elements are made variable andpaused to varysimultaneouslnby means o f'a single control 4', in such mannerto'keepthe 3 characteristic impedance of this line constant during thisvariation, and equal to Z, to wit: the characteristic impedance ofantenna 2.

The system may for instance include six cells consisting each of aninductance coil L in series and a capacitor C in shunt; the controlmeans for varying 'thesevalues are coupled together in such manner thatthe expression remains constant and is equal to Z.

Any suitable means may be used for controlling the variable inductancecoils and variable condensers from a Single control shaft (cams, coilsand condensers of special shapes, etc.) for ensuring the constancy ofexpression Of course, the number of cells-including each avariable-inductance coil and a variable capacitor-may vary. Calculationshows that, in order to obtain a very fine adjustment, six cells are tobe employed but that a lower number (as low as two in certain cases) maybe suflicient for obtaining a rough adjustment.

The variations being more important for long These features are adaptedto permit the adjustment of a dissymmetrical antenna 2 (Fig. 3). If nowit issupposed that it is desired to act upon a symmetrical or doubletantenna 5, 5 (Fig. 4), the artificial line will include two sets of inductance coils L in series connected two by two through balanced orsplit condensers C. In this case also the inductance coils and thecapacitors will be varied simultaneously and in such manner as to complywith the condition (characteristic impedance of the antenna) that is tosay, in fact, in such manner as to keep the values. of L and C in thesame ratio to each other. l v I 1 I may further couple together, with avariable coupling coefiicient M, homologous inductance coils in the twobranches of the artificial line. ,The values of L, C, M will be variedin such manner. as always to remain proportional to one another, inorder to comply with the condition of constancy of the characteristicimpedance of the artificial line thus constituted.

It is thus possible to act on a symmetrical or doublet antenna 5, 6(Fig. 4) from a dissymmetrical transmitter or line such as a coaxialcable 1. Reciprocally, a dissymmetrical antenna might be j acted uponfrom a symmetrical transmitter or line.

; .It is to be noted that, in most cases, a slight adjustment variationoccurs, due to the fact that 4 the value of the impedance of the pointof resonance increases when the wave-length that is chosen decreases;but this increase is small and most often can be neglected. As a matterof fact, when the antenna is attacked directly through a transmitter,the tubes work with the maximum .of power supplied for the impedancethat is utilized, and this power varies little with the wavelength, asany function close to a maximum; and when the antenna is attackedthrough a feeder with progressive waves which ends on its characteristicimpedance-which ensures the minimum of losses-these losses will remainsmall, as any function close to a minimum, if a slight unbalancing takesplace.

My tuning device has, over the already existing devices of the kind inquestion, among other advantages, that of performing the adjustmentvery'simply in a single operation.

The consecutive inductance coil elements could be coupled together, witha view in reducing the volumeof the apparatus.

In a general manner, while I have, in the above description, disclosedwhat I deem to be practical and efficient embodiments of my invention,it should be well understood that I do not wish to be limited thereto asthere might be changes made in the arrangement, disposition and form ofthe parts without departing from the principle of the present inventionas comprehended within the scope of the accompanying claims.

What I claim is:

1. For use with a radio transmitter antenna, a tuning device whichcomprises, in combination, feeder means including at least two variableinductance coils in series with said antenna and two variable capacitorsin shunt between the earth and said antenna, and control means forsimultaneously adjusting said coils and said capacitors to keep'theapproximate characteristic impedance of said feeder means, as expressedby the square root of the inductance to capacity ratio thereof,substantially constant and equal to the approximate characteristicimpedance of said antenna. j

2. For use with a radio transmitter doublet antenna, a tuning devicewhich comprises, in combination, feeder means including a line for eachan tenna element with at least two variable inductance coils in seriestherein and at least two variable balanced capacitors inserted in shuntbetween said lines, and control means for simultaneously adjusting saidcoils and said capacitors to keep a given proportional relation betweenthe respective inductances and capacities thereof, said control meansbeing adapted to keep the approximate characteristic impedance of saidfeeder means, as expressed by the square root of the inductancetocapacity ratio thereof, substantially equal to the approximatecharacteristic impedance of said antenna. I

3. For use with aradio transmitter doublet antenna, a tuning devicewhich comprises, in combination, feeder means including a line for eachantenna element with at least two variable inductance coils in seriestherein and at least two variable balanced capacitors inserted in shuntbetween said lines, means for coupling together with a variable couplingcoefilcient the respective inductance coils of said lines, and controlmeans for simultaneously adjusting said coils and said capacitorsandvarying said coupling to keep a given proportional relation betweentherespec tive inductances, capacities and couplin coeflicients, saidcontrohmeansbeingadapted to keep the approximate characteristicimpedance 'of Said-feeder means, as expressed by the square root o-f-theinductance to capecity ratio thereof,

" ta t q l to the, abproziimete character- 322 5 istic lfnpedance ofsaid antenna 1,998,322 FRANCOIS BABIN. 5 71 7 2,438,116 REFERENCES CITEDThe following references are of record in the Number file of thispatent: m 493,860

UNITED STATES PATENTS Name Date Muller May 8, 1934 Kaar Apr. 16, 1935Roosenstein Dec. 26, 1939 Dodds et a1. Mar. 23, 1948 FOREIGN PATENTSCountry Date Great Britain Oct. 17, 1938

